1. Technical Field
One or more embodiments of the present invention relate to a chopper type power converter that chops a DC power to convert the DC power into an AC power and a power conditioner provided therewith.
One or more embodiments of the invention relate to a power converter that suitably converts the DC power generated by a DC power source such as a photovoltaic cell and a fuel cell into the AC power interconnected to a system and a power conditioner provided therewith.
2. Related Art
Recently, from the viewpoint of protection of a global environment, power generation systems, such as a photovoltaic cell and a fuel cell, which have a little influence on the environment are actively developed.
In some power generation systems, a power conditioner converts a DC power from a DC power source such as the photovoltaic cell that generates the power into an AC power having a commercial frequency interconnected to a system. The converted AC power is supplied to a household load connected to a commercial power system, and an excess power reversely flows onto the system side when the power generated by the power source exceeds power consumption of the household load.
Generally the power conditioner used in the power generation system includes an inverter that converts the DC power generated by the photovoltaic cell into the AC power and a protection device that is used to perform the interconnection to the system. The power conditioner is classified into an insulating type in which a DC portion and an AC portion are electrically insulated by an insulating transformer and a non-insulating type in which the insulating transformer is not used. When the insulating type and the non-insulating type are compared to each other, the non-insulating type is widely used because the non-insulating type is superior to the insulating type in power conversion efficiency (for example, see Japanese Unexamined Patent Publication No. 2002-10496).
FIG. 18 illustrates a configuration example of a photovoltaic power system provided with a non-insulating type power conditioner.
A power conditioner 36 is operated while interconnected to a commercial power source 2.
The power conditioner 36 includes a smoothing capacitor 33 that smoothes a power-generation output from a photovoltaic panel 1, a PWM-control inverter 34, a filter 35 that includes a reactor and a capacitor, and a control circuit (not illustrated).
In the power conditioner 36, the smoothing capacitor 33 smoothes the power-generation output from the photovoltaic panel 1. An inverter 34 includes four switch elements 37 to 40 each of which includes a MOSFET connected in reversely parallel to a diode. In the power conditioner 36, the power-generation output from the photovoltaic panel 1, smoothed by the smoothing capacitor 33, is converted into the AC power synchronized with a commercial power system to output the AC power by switching control in which the switch elements 37 to 40 of the inverter 34 are turned on and off at a frequency as high as about 18 KHz. The power conditioner 36 supplies the AC power to a load (not illustrated) through the filter 35 or reversely flows the AC power onto the system side.
In the PWM-control inverter 34 included in the power conditioner 36, it is necessary that the DC power having a high voltage of, for example, about 800 V from the photovoltaic panel 1 be converted into the AC power by performing the switching operations of the switch elements 37 to 40 at the frequency as high as about 18 KHz. Therefore, unfortunately the power converter provided with the conventional power conditioner 36 has low power conversion efficiency because a large switching loss is generated during power conversion of the power conditioner 36.
One or more embodiments provide a power converter that enhances the conversion efficiency from the DC power into the AC power and a power conditioner provided therewith.